1. Field of the Invention
The present invention relates to an ink printing method and to an ink-jet printing system and, more specifically, to an ink printing method to conduct printing using a treating liquid for substantially insolubilizing a coloring material contained in ink and to an ink-jet printing system. The ink printing method and ink-jet printing system of the present invention can be applied to apparatus such as printers, copiers, or facsimiles for printing characters, images and the like on a printing medium such as paper, and used as a printing unit in these apparatus.
2. Related Background Art
The treating liquid for insolubilizing a coloring material such as a dye or pigment contained in ink is generally used to improve a water fastness of a printed image or the like. The present applicant has made various proposals, paying attention to the fact that the treatment solution not only improves the water fastness but also exerts a great influence upon printing qualities such as a density (for example, optical density (OD)) of a printed image and the sharpness of edge portions of a printed image. These printing qualities contribute particularly to the improvement of the quality of characters to be printed using a black ink in most cases.
As described above, printing using a combination of ink and a treating liquid can achieve high OD and high sharpness for the edge portions of an image, thereby making possible a high quality of printing that could not be attained in the prior art. However, an ink-jet printing system still has room for improvement of fixing ability, which has been discovered through studies conducted by the present inventor.
For example, to print a large number of printing paper sheets continuously, the printing paper sheets discharged after printing are placed one upon another sequentially. In this case, when the permeation of ink onto printing paper is insufficient and ink remains on the surface of the printing paper, the remaining ink is transferred to another printing paper and stains the printing paper. Thus, the paper discharge speed must be slowed down to prevent ink from staining another printing paper when ink fixing is slow regardless of the capability of a print head or the capability of a printing paper feed system. Therefore, the fixing ability of an ink-jet printing system is a relatively large factor for limiting the number of printing paper sheets to be output per unit time.
The present invention has been made in view of the above situation, and has an object to provide an ink printing method and ink-jet printing system capable of conducting printing with excellent fixing ability which cannot be attained in the prior art and at least one of printing qualities (qualities for maintaining the quality of characters in particular to a high level) such as OD and sharpness.
The above object can be achieved by the present invention described below.
According to the present invention, there is provided an ink printing method to apply an ink on a medium, comprising the step of combining an ink containing at least a self-dispersing pigment having a first group with a polarity as a coloring material with a treating liquid, wherein the treating liquid contains a surfactant having in the molecule one second group having a polarity opposite to that of the first group of the pigment.
According to the present invention, there is also provided an ink-jet printing system to conduct printing by combining an ink containing at least a self-dispersing pigment having a first group with a polarity as a coloring material with a treating liquid on the surface of a printing medium, wherein the treating liquid contains a surfactant having in the molecule one second group having a polarity opposite to that of the first group of the pigment.
According to the above constitution, the group of the pigment can be completely bonded to the group of the surfactant, thereby enhancing cohesive force between the pigment particles. As a result, a combined product of ink and the treating liquid shows a high penetrability and does not form a dispersion of fine aggregates, but can form large uniform aggregates.
Therefore, according to the present invention, at least one printing quality and excellent fixing ability can be secured.
The combination of xe2x80x9cinkxe2x80x9d and xe2x80x9ctreating liquidxe2x80x9d as used herein encompasses all the cases including one where they are combined on the surface of a medium and one where they are combined right before the surface of the medium or in space. Preferably, one of them is applied to paper and then the other is applied thereto, which are then combined with each other on the surface of paper. According to the object and effect of the present invention, ink or the treating liquid is preferably first applied to the paper. The reason for this will be understood from the following description.